<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>03计算器练习</title>
</head>
<body>
    <input type="text" placeholder="请输入数字1" id="i1"> <br>
    <input type="text" placeholder="请输入数字2" id="i2"> <br>
    <button onclick="calc('+')">加</button>
    <button onclick="calc('-')">减</button>
    <button onclick="calc('*')">乘</button>
    <button onclick="calc('/')">除</button>
    <h4>运算结果: <span></span></h4>
    <script>
        function calc(o){
            let n1 = document.getElementById('i1').value;
            let n2 = document.getElementById('i2').value;
            n1 = parseFloat(n1);
            n2 = parseFloat(n2)
            let spanE = document.querySelector('span');
            switch (o) {
                case '+':
                    spanE.innerHTML = n1 + n2 ;
                    break;
                case '-':
                    spanE.innerHTML = n1-n2;
                    break;
                case '*':
                    spanE.innerHTML = n1*n2;
                    break
                case '/':
                    if (n2!=0){
                        spanE.innerHTML = n1/n2;
                    }else {
                        alert('除数不能为0!');
                    }
            }
        }
    </script>
</body>
</html>